1. Field of the Invention
The present invention relates to organic EL panels, and particularly to an organic EL panel including an element substrate dehydrated at a shorter time and to a method for manufacturing the same.
2. Description of the Related Art
General organic EL elements that have recently been developed have a fundamental multilayer structure of an anode, an organic layer including at least a light-emitting layer, and a cathode. Light emitted from the light-emitting layer is extracted across a substrate, such as a glass plate, using a transparent anode formed on the substrate. In addition, active matrix panels that have driving transistors for each light-emitting pixel have been increasingly studied.
As the demand for high-definition images and low power consumption grow, it is expected that a low-cost, high-quality active matrix organic EL panel will be placed into practical use.
FIG. 1 is a schematic view of a typical conventional structure of an active matrix organic EL panel. As shown in FIG. 1, the active matrix organic EL panel has a plurality of transistors 12 on a substrate 11. A planarizing layer 13 is formed on the transistors 12. A plurality of anodes 15 are connected to the respective transistors 12 through contact holes 14, and a separation film 16 covers the edges of the anodes, defining apertures for the anodes. Furthermore, an organic layer including at least a light-emitting layer 17 and then a cathode 18 are formed over the separation film 16. A current controlled by the drive circuit of each transistor is supplied to the corresponding anode and delivered to the light-emitting layer and the cathode. Electroluminescence is thus produced.
The planarizing layer 13 covers the unevenness of 0.1 to 1 μm in height resulting from the formation of the plurality of transistors 12 and maintains a smooth surface of the element substrate.
The planarizing layer 13 is formed of an organic resin, such as acrylic resin, by spin coating.
The separation film 16 is intended to protect the edges of the patterned anodes 15, and is formed of an organic resin, such as polyimide resin, by spin coating.
Alternatively, the separation film 16 may be formed of an electrically insulating inorganic material, such as silicon nitride, silicon oxide, SiON, or aluminum oxide by magnetron sputtering, high-frequency ion plating, chemical vapor deposition (CVD), or the like.
It has been known that organic EL elements are not water-resistant. The organic materials used for the organic EL element are liable to be decomposed or altered by water or solvents and, consequently, can result in problems, such as occurrence of a dark spot or decrease in luminance around pixel edges or during high temperature storage.
Furthermore, if the planarizing layer 13 is formed of an organic resin, then the layer 13 contains a relatively large amount of water after being spin coated and patterned. In addition, more water is added to the planarizing layer 13 when patterning the pixel electrodes, or the anodes 15, on the planarizing layer.
If the light-emitting layer is formed on the hydrated planarizing layer 13, the light-emitting layer absorbs water, and consequently, a dark spot occurs or the luminance is reduced. It is, therefore, required that dehydration of the planarizing layer 13 be performed by baking it at a high temperature before forming the light-emitting layer (Japanese Patent Laid-Open No. 2003-332058).
Unfortunately, in order to prevent reductions in luminance of the organic EL element, dehydration needs to be conducted for a sufficient time. Accordingly, a prolonged dehydration step is disadvantageous to productivity.
The dehydration of the planarizing layer is prolonged due to the presence of the metal electrode or anodes over the planarizing layer which blocks the primary route of dehydration.
If the separation films are formed of an organic material, the water exiting the planarizing layer enters the separation films through small areas of the planarizing layer in contact with the separation films and passes through the separation film to escape. Thus, the dehydration step is further prolonged.
If the separation film is formed of an electrically insulating inorganic material, such as silicon nitride, silicon oxide, SiON, or aluminum oxide, it is more difficult to transmit the water through the separation film than the case in which an organic separation film is used. Hence, the dehydration of the planarizing layer is even more difficult when employing an insulative inorganic material. Furthermore, the confined water transiting the separation film may expand and crack the separation film.